The present invention relates primarily to improvements in the prevention of foreign particle blockage of the small pilot passages in pilot operated valves where the pilot actuator controls flow through an orifice to create pressure differential forces across a flexible diaphragm which acts as a main valve to permit and prevent flow through the main flow ports. These types of valves are economical in cost and are used in many applications and the state of art of their operation is well known, as is their susceptibility to malfunction when their relatively small pilot passages become blocked by foreign particles or other contaminants.
Special attention is therefore paid to provide the best possible means for protection of these pilot flow sections from foreign particle contamination. Use of wire screening at the main flow inlet port does not offer full protection for these pilot passages as this screen size is necessarily made large to only trap major particles as a smaller mesh screen would fully clog in very short operational time intervals. The inlet flow screens are therefore compromised to allow passage of foreign particles that can enter the pilot flow section and cause overall valve malfunction. To overcome this difficulty, these valves have been fitted with an additional pilot valve section screening means which prevents the smaller foreign particles which have passed through the main inlet flow screen to enter and block the pilot sections. An example of this screen means is shown in U.S. Pat. No. 3,672,627 by McCarty et al, where the screening means is provided by a plurality of small holes formed through the diaphragm before flow entry to the pilot section. A more recent example are U.S. Pat. No. 4,844,112, 4,981,155, and 5,145,145 by J. Pick, et al, where pilot screen means are provided by circumferentially placed groves within a valve cavity and with a mating member forms a plurality of small grooved openings where pilot fluid may flow and may effectively trap foreign particles. The merits of the screen means given by Pick indicate some superior advantages over that shown by McCarty, however, the Pick design would still seem to have particular deficiencies in the dimensional tolerance control of the illustrated circumferential bleed passages, the ability to clean the pilot valve screening, difficulty in adopting this means to other than plastic body valves, and its probable high cost. In addition, both the McCarty and Pick approaches require screen passage sizes smaller than the bleed hole to effectively provide valve foreign particle protection. The necessity to provide the very small screen passages as usually required by the single small bleed hole size make both of these approaches somewhat difficult to attain.
To overcome the difficulties of the prior art described, the objectives of this invention are to: (1) provide a pilot valve having improved screen dimensional size tolerance control, be removable for field service cleaning, and be adaptable for use with either plastic or metal valve bodies, and (2) have provision for an enlarged pilot flow passage means which would permit the use of larger pilot screen passages for ease of manufacture, cost effectiveness and possess the overall ability to prevent a pilot valve passage blockage that would cause a failure to close of the main valve member.
The present invention focuses primarily on two basic methods to prevent foreign particle orifice passage blockage of a pilot operated valve that controls differential pressures across a pressure sensitive member such as a diaphragm having a poppet seat to open and close a main flow port of the valve. As is well understood by those knowledgeable in the state of the art of these valves, a blockage of the upstream orifice or bleed orifice of this pilot flow passage will cause a failure to close condition of the main valve port and could thereby lead to flooding and property damage. On the other hand, a blockage of the downstream or pilot actuator orifice results in a failure to open or a closed main valve position, and although not desirable, is not usually as serious as with a blockage of the upstream orifice. Agrevating the possible failure to close problem is that the upstream orifice is, by diaphragm operation necessity, made smaller than the downstream pilot actuator orifice and is therefore the most susceptible to foreign particle blockage. To overcome this major problem, one method utilized in the present invention provides a screening means which will only permit passage of particles small enough to harmlessly pass through the upstream pilot orifice and another method provides a means whereby this upstream orifice has been enlarged so that it no longer is the minimum pilot passage area and therefore becomes less prone to the foreign particle blockage condition. In the screening method, an arrangement of small screening passages are formed between the periphery of the diaphragm seal and the valve body while another screen version utilizes a removable plastic screening member to facilitate its fabrication and service cleaning and can also be adapted to either a plastic or metal body. In the latter version, the screen passages are formed between the valve body and the removable member which is sandwiched between the outer peripheral seal of the diaphragm and valve body. In still another version, the screening passages are formed in the central portion of the flexible diaphragm. In all versions the means whereby the screen passages are formed permit a very precise dimensional tolerance control and thereby assure proper foreign particle screening of the pilot flow orifice passages.
A second approach toward minimizing pilot valve foreign particle orifice blockage utilizes a series connected enlarged orifice passages which together produce an equivalent pressure drop of a single small orifice. By this arrangement, a larger bleed hole passage can be used which results in a much larger orifice passage area and thereby makes this passage much less likely to become blocked and also permits the use of less critical and larger size screen passages. In addition, the series orifice passage diameters can tolerate considerably more tolerance variability than that allowed for a single bleed orifice and thereby also improves the dimensional control of the pilot valve bleed orifice. In the series orifice passage embodiment, three versions are illustrated, one provides the passages in the peripheral rim of the diaphragm, a second version provides these series passages in a separate elastomeric ring, and a third version illustrates the series connected passages in the central portion of the diaphragm. In the second and third versions, the series bleed passages can be placed downstream of the screening passages to add an extra protective margin against possible foreign particle blockage of the bleed passage. The series orifice bleed passages provide the simplest means to attain the larger bleed passages, but a further enlargement of these passages may be achieved by the addition of a vortex flow means with each series orifice. Vortex flow restrictors add an extra pressure drop to a simple orifice and are well known configurations by persons familiar in the state of the art of fluid flow and are therefore not more fully explained or illustrated but are mentioned as an option to add extra pressure drop to the series orifice passages if needed in an application of the invention.
Whether the series connected passages are simple connected orifice passages or of the vortex configurations, and the screen means are of various patterns, all of these configurations can be suitably manufactured and can thereby be economically incorporated into a pilot operated valve assembly.
In some applications, foreign particle protection may not be a critical condition and in these cases the series connected pressure drop passages could be dimensionally the same as that used in a single orifice but would result in a greater pressure differential across the pressure responsive main valve member. This would permit use of a smaller diameter pilot valve seat and thereby reduce the required actuation lift force which in turn would permit the use of a more economical pilot valve actuator. The improved series connected passages so sized and combined with the improved screening means described previously would provide additional benefit of the described invention.
Therefore, the present invention as described, has thus achieved its objectives of improving a pilot operated valve assembly for improved resistance against foreign particle bleed passage blockage by: (1) an improved pilot screening means, (2) an enlarged bleed orifice passage less susceptible to foreign particle blockage, (3) provision to permit removal of foreign particle screen means for service cleaning, (4) providing an improved dimensional control of the pilot bleed passage, and (5) the capability to incorporate the foreign particle protection improvements into either plastic or metal valve bodies.